Integrated optical communication and range finding system and application thereof

ABSTRACT

The present invention is directed toward systems for conducting laser range and enabling optical communication between a plurality of entities and to the application of such systems in a secure covert combat identification system. In one embodiment, the present invention uses a novel laser system that generates high pulse rates, as required for optical communications, while concurrently generating sufficiently high power levels, as required by laser range finding operations. One application of the present invention is in enabling secure covert communications between a plurality of parties. Another application of the present invention is in tracking and identifying the movement of objects.

CROSS-REFERENCES TO RELATED APPLICATIONS

This invention is a continuation of co-pending application Ser. No.10/462,006 filed on Jun. 13, 2003, which is a continuation-in-part ofapplication Ser. No. 10/066,099, now U.S. Pat. No. 7,308,202.

FIELD OF THE INVENTION

The present invention relates to optical systems, and, morespecifically, to systems for conducting laser range and enabling opticalcommunication between a plurality of entities and to the application ofsuch systems in secure covert combat identification systems and objecttracking systems.

BACKGROUND OF THE INVENTION

For various applications, including surveying, engaging in combat, andtracking objects, it is often necessary to determine the distance ofremotely located objects and to communicate with a third party that maybe proximate to the remotely located object. Conventionally, suchfunctionality has been achieved using two separate systems that havebeen either physically combined into a single operating unit orseparately provided into two physically distinct operating units.

For example, one approach to determining a distance to a remote objectis to measure the time of flight of a pulse of light from the measuringsystem to the object and back again, and, subsequently, to calculate thedistance to the object based upon the speed of light and differences inthe transmitted and received light. Systems employing this methodtypically employ a laser to generate the light pulse and are knowngenerically as “laser range finders” (LRFs) or “light detection andranging” (LiDAR) systems.

The accuracy and resolution of a LRF system, along with the maximumrange that can be dependably measured by such systems, are dependent ona plurality of factors. For example, the laser pulses received afterreflection from a target comprise a replica of the transmitted laserpulse signals along with undesirable signals or noise making itdifficult to detect the signals of interest. Further, the laser pulsestransmitted and received after reflection from the target undergosignificant attenuation due to factors such as the nature of the surfaceof reflection of the target, atmospheric conditions and the distance ofthe target from the ranging system. Typically, LRF systems optimizeoperational efficiency by using high powered lasers, such as YAG solidstate lasers, that transmit using intermittent pulses of high power,such pulses often being separated by a minimum recharge period ofseveral milliseconds.

Data communications may be enabled by numerous devices and systems, fromsatellite transceivers, to mobile phones, to conventional PSTNconnections, to packet-based network communications. Applications thatrequire a high degree of data security and must operate in situationsand locations that may not have a reliable, or even an existent,telecommunications infrastructure have conventionally relied on someform of point to point optical communication. Such systems use a opticaltransmitter, such as a laser, in combination with a retroreflector toreceive a laser transmission and modulate a return signal.

These conventional optical communication systems have substantialdisadvantages, however. Because an optical communication system needs toachieve a sufficiently high data in order to be able to modulate, andtherefore communicate, meaningful amount of data, these systems rely onlasers having different operational characteristics, as compared tolasers conventionally used in LRF systems. Specifically, conventionaloptical communication systems use lower power, higher pulse rate lasersthat require a fraction of the recharge required by higher power lasers.Consequently, such systems can not be integrated with conventional laserrange finding systems.

Additionally, high data communication rate requires responsiveretroreflectors in order to enable a sufficiently modulation rate.Without a sufficiently responsive retroreflector, high modulation ratescan not be achieved and, consequently, high data communication rates cannot be effectuated, even if the appropriate laser system is utilized.U.S. Pat. No. 4,887,310 discusses identification devices having meansfor modulating a reflected laser beam at the target. However, thedisclosed systems are very expensive and not sufficiently sensitive.U.S. Pat. No. 4,134,008 discloses a method for transmitting a responsecode to an interrogation received at the location of the retroreflector.Kerr or Pockels cells, or PLZT ceramics(lead-lanthanum-zirconium-titanium), are used in the above-mentionedsystem for modulating the retroreflector signal. These modulatorsrequire high operating voltages and either very costly or allow for arelatively low modulation frequency.

In light of the abovementioned disadvantages, there is a for anintegrated optical communication system facilitating remote datacommunications and for a laser range finding system for determining thedistance of a remote object. There is also a need for enabling the useof a single laser system for both laser range finding and opticalcommunications. Furthermore, there is a need for retroreflector systems,and methods of use, that enable the sufficiently fast modulation of adata signal.

There is also a need to have an integrated laser range finding and datacommunication system adapted for use in military operations,particularly in secure covert operations. Military forces have aninterest in the remote and secure identification of a person, duringcombat training exercises and in armed conflicts, and in the trackingand identification of objects. Identification as friend or foe (IFF)systems are well-known in the art for military aircraft and otherweapons systems. Such systems are useful for preventing action againstfriendly forces. The military platform commanders on a modernbattlefield must accurately identify potential targets as friend-or-foe(IFF) when detected within range of available weapon systems. Suchtarget IFF presents a difficult decision for a military platformcommander, who must decide whether to engage a detected target whileavoiding accidental fratricide. This problem is even more difficult forthe dismounted soldier who may be moving covertly through an unknowncombat zone at night with limited visibility. Simple visual assessmentsof other dismounted soldiers is not a reliable IFF method for militaryplatforms or dismounted infantry.

The art is replete with proposals for IFF systems for military platformsin modern land battlefields. But commanders often still rely onlow-resolution visual and infrared images to identify detected targets.Commanders often must operate under radio silence to avoid detection byan enemy. With infrared (IR) imagers alone, the identification ofindividual dismounted soldiers is not feasible, although the IRsignatures of land vehicles may have some use. IFF systems that requireone or more radio signals are limited in channel-capacity and must bearthe overhead of selecting and/or awaiting an available battlefieldchannel before completing the IFF task. Active-response systems requirethe emission of a signal by the unknown respondent in response to averified challenge, which may compromise the security of bothinterrogator and respondent. Active transponders are subject to captureand may be used for spoofing by the enemy in a battlefield or a combattraining environment. Passive response systems rely on the return of anecho (reflection) of a challenge signal to the interrogator, but simplereflection schemes are easily compromised and more elaborate passivereflection schemes are still subject to intercept, compromise or capturefor use by the enemy in spoofing the interrogator.

As described in U.S. Pat. No. 4,851,849 by Otto Albersdoerfer, a typicalactive IFF technique for vehicles is to equip a military vehicle with atransponder that emits a coded return signal when an interrogating radarpulse is detected by its receiver. As described in U.S. Pat. No.5,686,722 by Dobois et al., a more sophisticated active IFF techniquefor vehicles uses a selective wavelength optical coding system withtunable optical beacons mounted on each vehicle. By spreading theoptical broadcast energy into frequency in a precise manner, the beaconidentifies the host vehicle to friendly receivers while remaining covertto the enemy.

As described in U.S. Pat. No. 4,694,297 by Alan Sewards, a typicalpassive IFF technique for vehicles is to equip a military vehicle with apassive antenna that reflects an interrogatory radar beam while adding adistinctive modulation by varying the antenna termination impedanceresponsive to evaluation of the interrogatory beam. A more sophisticatedpassive electro-optical IFF system for vehicles is described in U.S.Pat. No. 5,274,379 by R. Carbonneau et al., wherein each friendlyvehicle is provided with a narrow-beam laser transmitter and a panoramicdetector. If a vehicle detects a coded interrogator laser beam andidentifies the code as friendly, it opens a blocked rotatingretroreflector to clear a reflection path back to the source, where itcan be identified by another narrow field-of-view detector. A furthermodulation is also added to the reflected beam to identify thereflecting vehicle as friendly. If an improperly coded beam is detected,the transmission path is not cleared, thereby preventing reflection ofthat beam and warning is sent to the vehicle commander of an unfriendlylaser transmission. Others have proposed similar passive optical IFFsystems for vehicles, including Wooton et al. in U.S. Pat. No. 5,459,470and Sun et al. in U.S. Pat. No. 5,819,164.

The art is less populated with IFF proposals for the lone dismountedsoldier (the infantryman on foot). Whether in actual combat or in atraining exercise, the dismounted soldier operates with severe weightlimits and little onboard electrical power. The friendly foot soldierhas no distinctive acoustic, thermal or radar cross-section that may beused to assist in distinguishing friendlies from enemies. But somepractitioners have proposing IFF solutions for the dismounted soldier,both active and passive. For example, in U.S. Pat. No. 6,097,330, Kiserproposes an active IFF system for identifying concentrations of groundtroops (or individuals) from an aircraft by interrogating a (heavy)human-mounted radio transmitter carried by one of the group with anarrow-cast optical signal. As another example, in U.S. Pat. No.5,299,277, Rose proposes a compact active IFF system to be carried byeach individual dismounted soldier for use in combat exercises or on thebattlefield. The system includes a clip-on beacon and a hand-held(flashlight-style) or weapon-mounted detector. The beacon radiates aspread-spectrum low-probability-of-intercept (LPI) signal at opticalfrequencies that are selected to be invisible to the usual detectorspresent in the battlefield. Rose doesn't consider the problem ofspoofing with captured devices. As yet another example, in U.S. Pat. No.5,648,862, Owen proposes an active IFF system implemented by addingprovisions for coded two-way transmissions to the night-vision systemsoften worn by dismounted soldiers. As a final example, in U.S. Pat. No.5,966,226, Gerber proposes an active combat IFF system for eachdismounted soldier that includes a weapon-mounted laser projector forinterrogating suspected targets and a harness including means forreceiving the interrogatory signal and means for responding with anencoded radio, acoustic or optical signal.

These proposals do not resolve, however, the spoofing problem (throughcapture of a beacon or harness, for example); and are not particularlycovert because the responding target generally broadcasts an activesignal either continuously or in response to interrogation. Any IFFproposal employing broadcast signals also faces a battlefield channelcapacity (or channel ability delay) problem as well. Furthermore, theseproposals do not address the need to be able to actually communicatewith a target to verbally identify the individual as a friend or foe.

There is still a need in the art for a secure cover system (SCS) forthat provides true passive covertness and that cannot be spoofed underany battlefield conditions. The desired SCS system requires little powerand is adapted to prevent any use of captured equipment or interceptedsignal codes. Furthermore, the desired SCS system is capable of enablingboth range finding an optical communication functionality in thelightest weight configuration possible. Finally, the system should beinexpensive enough to permit equipping every soldier with the necessaryinterrogation and response equipment for combat exercises or actualbattlefield conditions.

These unresolved problems and deficiencies are clearly felt in the artand are solved by this invention in the manner described below.

SUMMARY OF THE INVENTION

The present invention is directed toward systems for conducting laserrange and enabling optical communication between a plurality of entitiesand to the application of such systems in a secure covert combatidentification system. In one embodiment, the present inventioncomprises a laser system for determining range values and enablingcommunications between a plurality of parties, comprising a laser forgenerating a plurality of transmission pulses wherein said laser isactivated by a first party; an optical transmission system for directingthe transmission pulses emitted by the laser on to a target objectwherein said transmission pulses are reflected by the target object tocreate reflected signals, an optical reception system for receiving saidreflected signals; and a processor for deriving range data andcommunication data from said reflected signals.

Optionally, the communication data includes any one of audio, video,text, or image data. The optical transmission further comprises acollimator. The laser is a fast pulsed laser, wherein the laser is anyone of a mode-locked visible-range titanium-doped sapphire laser, Kerrlens mode-locked laser, polarization-sensitive mode-locked fiber laser,or actively mode-locked laser. Preferably, the laser is a masteroscillator power amplifier device and further comprises an opticalamplifier medium, preferably being an erbium-doped fiber amplifier.

Optionally, the optical reception system comprises an analog board, anAPD receiver module, a receiver lens, a filter assembly, and a receiveraperture into which the reflected signals are received. Optionally,range data is displayed on a range display. Optionally, the laser systemof claim 1 further comprising a light sensitive detector, a change-overmodule, and a correlator module. Optionally, the correlator modulecomprises a memory for storing a plurality of coded pulse sequences fortriggering the laser, and for storing the reflected signals, whereinsaid reflected signals are digitized by an analog-to-digital convertercoupled to the reception system, and a processor for calculating a rangeof the target object by correlating the reflected signals with thetransmitted pulses and estimating a time delay of the reflected signalsat which the correlation between the transmitted pulses and reflectedsignals is maximum.

Optionally, the processor further calculates best lines-of-fit for apredetermined number of sample points before and after a maximum pointof correlation to determine a revised maxima. Optionally, the laser istriggered by coded pulse sequences read out from a memory at apredetermined clock frequency. Optionally, the coded pulse sequence fortriggering the laser is of a pseudo random binary type. Optionally, thecoded pulse sequence for triggering the laser is encoded using a MaximalLength Sequence.

In another embodiment, a method of the present invention comprises thesteps of generating transmission pulses at fast rates by triggering alaser using coded pulse sequences read out from a memory at apredetermined clock frequency, storing the coded pulse sequences fortriggering the laser, directing the transmission pulses on to the targetobject, receiving the reflected pulses from the target object,digitizing the received reflected pulses, storing the digitizedreflected pulses, and calculating the range of the target object bycorrelating the reflected pulses with the transmitted pulses andestimating a time delay of the reflected pulses at which a correlationbetween the transmitted and reflected pulses is maximum.

In another embodiment, a method of the present invention comprises thesteps of generating transmission pulses at fast rates by triggering alaser using coded pulse sequences read out from a memory at apredetermined clock frequency, modulating a signal onto saidtransmission pulses, directing the transmission pulses from the firstentity to the second entity, receiving the transmission pulses at aplurality of retroreflectors proximate to the second entity, modulatinga response onto reflected signals, receiving said reflected signals, andextracting range data and communication data from said reflectedsignals.

Optionally, the retroreflector comprises any one of a polymer dispersedliquid crystal, a ferro-based liquid crystal, amicro-electrical-mechanical system, or multiple quantum wells.Optionally, the retroreflector is heated upon activation by atransmission pulse.

In another embodiment, a method of the present invention comprises thesteps of generating transmission pulses at fast rates by triggering auser using coded pulse sequences read out from a memory at apredetermined clock frequency, modulating a transmit code onto saidtransmission pulses, directing the transmission pulses from the firstentity to the second entity, receiving the transmission pulses at aplurality of retroreflectors proximate to the second entity, modulatinga response code onto reflected signals, receiving said reflectedsignals, and extracting range data and code data from said reflectedsignals.

In another embodiment, the present invention includes a laser system fordetermining range values and enabling communications between a pluralityof parties. The laser system comprises a laser for generating aplurality of transmission pulses, an optical transmission system fordirecting the transmission pulses emitted by the laser on to a targetobject wherein said transmission pulses are reflected by the targetobject to create reflected signals, an optical reception system forreceiving said reflected signals, and a processor for deriving rangedata and communication data from said reflected signals wherein saidreflected signals are subjected to an autocorrelation function.

In another embodiment, a method of the present invention comprises thesteps of generating a plurality of transmission pulses using a fastpulsed laser, directing the transmission pulses emitted by the laser onto a retroreflector wherein said transmission pulses are reflected bythe retroreflector to create reflected signals, receiving said reflectedsignals, and processing range data and communication data from saidreflected signals wherein said reflected signals are subjected to anautocorrelation function.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference is nowmade to the following detailed description of the embodiments asillustrated in the accompanying drawing, in which like referencedesignations represent like features throughout the several views andwherein:

FIG. 1 is a flowchart depicting one embodiment of the laser rangefinding system of the present invention;

FIG. 2 a is schematic of one embodiment of a circuit for the generationof a signal;

FIG. 2 b is a chart of voltages for a plurality of received signals;

FIG. 3 is a chart of an exemplary calculated correlation betweentransmission and reception signals;

FIG. 4 is a visual representation of an assembly of one embodiment ofthe laser range finding system of the present invention;

FIG. 5 is a view of one embodiment of a laser system of the presentinvention in physical communication with a weapon;

FIG. 6 is a schematic diagram of an exemplary polymer-dispersed liquidcrystal cell;

FIG. 7 depicts a plurality of configurations of a liquid crystal basedretroreflector;

FIG. 8 depicts a plurality of alignment states in an exemplary liquidcrystal sample;

FIG. 9 is a block diagram of an exemplary retroreflector/obturator;

FIG. 10 depicts one embodiment of an exemplary ferroelectric liquidcrystal based retroreflector;

FIG. 11 depicts an exemplary arrangement of a MEMS device;

FIG. 12 depicts an exemplary arrangement of a MEMS device uponapplication of an electric field;

FIG. 13 depicts an MEMS device operating as an retroreflector/obturator;

FIG. 14 depicts an exemplary embodiment of a multiple quantum well;

FIG. 15 is a sketch illustrating the operation of the combatidentification system of this invention;

FIG. 16 is a schematic diagram illustrating the optical operation of acombat response unit of the present invention;

FIG. 17 is a schematic block diagram illustrating the logical operationof a combat response unit of the present invention;

FIG. 18 is a schematic block diagram illustrating the logical operationof a combat interrogatory unit of the present invention;

FIG. 19 is a chart illustrating the relationship between examples of thecode of the day (COD), the transmitted code of the day (TCOD) and theresponse code of the day (RCOD) according to one method of thisinvention;

FIGS. 20( a)-(d) are sketches illustrating several examples of means foraccepting biometric data employed in a combat response unit of thepresent invention; and

FIG. 21 is a block diagram of a flow chart illustrating a method of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward systems for conducting laserrange and enabling optical communication between a plurality of entitiesand to the application of such systems in a secure covert combatidentification system. In one embodiment, the present invention uses anovel laser system that generates high pulse rates, as required foroptical communications, while concurrently generating sufficiently highpower levels, as required by laser range finding operations. Oneapplication of the present invention is in enabling secure covertcommunications between a plurality of parties. Another application ofthe present invention is in tracking and identifying the movement ofobjects. The present invention will be described with reference toaforementioned drawings. One of ordinary skill in the art wouldappreciate that the applications described herein are examples of howthe broader concept can be applied.

Integrated Laser Range Finding and Optical Communications

Referring to FIG. 1, a functional block diagram of a laser system 100 ofthe present invention, when operating as a range-finder, is shown. Thelaser system comprises a laser 110, an optical transmitter 120, anoptical receiver 130, a light, sensitive detector 140, a change-over anda correlator module 150. The correlator module 150 further comprises aclock signal generator 165 that provides working clock signals to ananalog-to-digital converter 170, a counter 160 for addressing andsequencing a memory module 155 and a processing unit 175. The memorymodule 155 stores digitized values of a sequence of transmission pulsess(t), for triggering the laser 110, as well as reception pulses r(t)outputted from the detector 140 and digitized by the analog-to-digitalconverter 170.

The laser 110 is a source of short pulses of electromagnetic energy. Thelaser is preferably driven by an ultra-fast pulsed laser oscillator suchas a mode-locked visible-range titanium-doped sapphire laser, Kerr lensmode-locked lasers, polarization-sensitive mode-locked fiber lasers,actively mode-locked lasers or any other suitable laser source known topersons of ordinary skill in the art. In one preferred embodiment, thelaser source 110 is a master oscillator power amplifier (MOPA) devicecomprising a master oscillator (MO) semiconductor laser diode having anoutput facet optically coupled to or formed integral with an opticalpower amplifier (OPA). A monolithic MOPA device has been described inU.S. Pat. No. 4,744,089 to Montroll et al. and is hereby incorporated byreference.

In a preferred embodiment, rare earth elements (example, erbium) in anoptical amplifier medium or a rare earth-doped fiber section (example,an erbium-doped fiber amplifier also termed as EDFA) are excited by apump light source using a laser diode, so that a signal light cominginto the EDFA section causes induced emission by the excited rare earthelement. Such an EDFA based system has been described in U.S. Pat. No.6,064,514 to Aoki et al. and is also hereby incorporated by reference.

Referring to FIG. 4, a visual representation of one embodiment of alaser range finding system 420 is shown. A laser emits optical signalsthrough a collimator 410 which collimates the beam for subsequenttransmission through a laser aperture 405. Power is supplied to the unitby battery 480. The system further comprises a HV supply 430, an analogboard 440, an APD receiver module 450, a receiver lens and filterassembly 460 and a receiver aperture 470 into which reflected opticalsignals are received. The resulting range is depicted on a range display420.

Laser system 100 of FIG. 1 may be built as stand alone hand held unitsor embodied in larger systems. The laser system may be incorporated intotanks, planes, vehicles, armored trucks, carrying cases, backpacks,hand-held weapons, guns, and other devices. For example, FIG. 5 shows aMOPA/EDFA-based LRF system 500 mounted upon a shotgun barrel SILO.

For range finding, the transmission pulse sequences s(t), stored in thememory module 155, are read out, using the counter 160, which is actedupon by the clock signal from the clock signal generator 165, and sentto the laser 110 causing the laser 110 to emit a pulse of light at timet0. This pulse of light is focused by the transmission optics 120 andtravels to a target object 180 where it is reflected by aretroreflector/obturator (not shown).

The function of a retroreflector is to receive input electromagneticenergy and to reflect it back along the same or parallel path,preferably with similar general characteristics and preferably withrelatively high gain and little spreading of the light beam. Thereceiving optics 130 collects a portion of the reflected light pulsesand focuses them onto the light sensitive detector 140. The detector 140converts the received light pulse into an electrical signal output attime t1 and amplifies the electrical signals, if necessary. Theseelectrical signal outputs are supplied to the analog-to-digitalconverter 170 that generates corresponding sequence of digital valuesr(t) which are then stored in the memory module 155. The digitaltransmission and reception signals, s(t) and r(t), respectively, arecommunicated to the processor unit 175, which calculates and displaysthe range to the target object 180 based upon the time of flight of thelaser pulse (t1-t0) and the speed of light c in the intervening medium.

The counter 160 and the analog-to-digital converter 170 are acted onsynchronously by the clock signal such that whenever a digital values(t) from the memory module 155 is read-out and transmitted by thetransmission optics 120, the analog value delivered at the same instantfrom the detector 140 is converted into a digital value r(t) and storedin the memory module 155. Consequently, after one transmission andreception cycle, signals of substantially the same shape are present inthe memory module 155 wherein the received signal r(t) is shifted intime relative to the transmitted signal s(t) by the time of flight(t1−t0) along the path of measurement, corresponding to a specificnumber of clock cycles.

The processor unit 175 derives the number of clock cycles correspondingto the time of flight (t1−t0) by calculating a correlation function k(t)between the transmission signals s(t) and the reception signals r(t),stored in the memory module 155. In accordance with the understanding ofpersons of ordinary skill in the art, the correlation function k(t)values are calculated, in each case, by summing the products ofoppositely disposed supporting position values of the two signals, s(t)and r(t), respectively. Thereafter, the maximum Kmax=k(tmax) of thecorrelation function k(t) is determined where the tmax represents thetime of flight at which the transmission and reception signals, s(t) andr(t), are time shifted relative to one another to an extent that theircurves have a minimum spacing from one another or substantially overlap.This shift corresponds to the time of flight or the number of clockcycles that have elapsed between the transmission and reception signalss(t) and r(t), respectively. Since the reception signals r(t) arereplicas of the transmission signals s(t) but delayed in time, personsof ordinary skill in the art would appreciate that the correlationoperation between the two signals corresponds to a condition ofautocorrelation.

In order to provide a distinct autocorrelation function values, thesequence of digitized transmission pulses s(t), stored in the memorymodule 155, are of the recurrent pulse type that may be channel-codedusing Barker binary codes, pseudo-random codes, Gold or Kasami code orany other suitable code known in the art. In a preferred embodiment, thetransmission pulses s(t) are encoded using a Maximal Length Sequence(MLS), which is a family of pseudo random binary signals typicallygenerated using a digital shift register whose input is generated fromappropriate feedback taps.

Alternatively and/or additionally, the MLS code pulses may be pulseposition modulated for data transmission. The MLS has suitableautocorrelation properties and since the signal takes values of +1 and−1, the autocorrelation may be computed using additions andsubtractions, without the need for multiplications. FIG. 2 a shows anexample of a MLS signal 240 a generated by a four-stage shift register200 a that receives clock information from a clock source 210 a anddata. Alternative length sequences can be generated by using longershift registers with appropriate feedback taps.

FIG. 3 shows a section from the calculated correlation function valuesk(t) between the transmission and reception signals s(t) and r(t),respectively. Five supporting values of the correlation function k(t)have been emphasized in FIG. 3, with the middle one of these five valuesrepresenting the maximum tmax. In order to further improve the timeresolution and obtain more accurate time of flight or lag-maxima tmax,the coefficients m1 and c1 for the best line-of-fit equation,s1(t)=m1·t+c1, are calculated (through a predetermined number of samplesprior to the tmax value) along with the coefficients m2 and c2 for thebest line-of-fit equation, s2(t)=m2·t+c2, through a predetermined numberof samples after the tmax value. These lines of best fit are shownplotted on FIG. 3. The intersection value t′_(max) can now be computedas:

t′ _(max)=[(c2−c1)/(m1−m2)]

where t′_(max) is a new time of flight value obtained at a higherresolution. The distance to the target object can be calculated from thedetermined t′_(max); it is half the speed of light multiplied by thetime-of-flight t′_(max).

However, the calculated value of the time-of-flight t′_(max) comprisesthe sum of the time-of-flight of light pulses transmitted and the signaltransit time. The signal transit times represent measurement errors thatcan, for example, be eliminated by the use of a reference signal.Referring back to FIG. 1, a reference signal 105 as well as thereception signal r(t) 106 are shown as inputs to the changeover switch185 for the selective coupling of the reference signal 105 and receptionsignal 106 to the correlator module 150. The changeover switch 185 hastwo switch positions, of which one is ‘reference,’ associated with thereference signal 105 and the other is ‘normal’ associated with thereception signal 106. When the switch position is ‘normal,’ thereception signals r(t) 106 are correlated with the original transmissionsignals s(t) in the correlator module 150 to determine thetime-of-flight t′_(max). However, when the switch position is‘reference,’ the reference signals 105 are correlated with thetransmission signals s(t) in the correlator module 150 therebydetermining the signal transit time error t_(error) within the LRFsystem 100. This transit time error t_(error) can then be subtractedfrom the time-of-flight value t′_(max) for error correction.

The present laser range finding system can also be used as an opticalcommunication system. Conventionally, laser range finding systemsemployed lasers, such as YAG solid state lasers, having substantialrecharge times, on the order of several milliseconds, in order toachieve the power levels required for effective laser range finding.With the novel approach described above, lasers having very high pulserates, such as a MOPA/EDFA laser assembly, can be used to conduct laserrange finding. Consequently, the same laser assembly can be used togenerate the requisite pulse rate for data communications. The lasersystem, as shown in FIG. 1, therefore employs a modulation scheme tomodulate the optical signal. As previously discussed, in one embodiment,pulses are pulse position modulated for data transmission.

To enable effective data communications, it is preferred that aretroreflector/obturator capable of rapid modulation is used. Thepresent invention is not limited to a specific type ofretroreflector/obturator and may employ any useful retroreflector deviceknown in the art, such as, for example, a Tech Spec™ Corner CubeRetroreflector (Trihedral Prisms) available from Edmond IndustrialOptics, Barrington, N.J. The obturator portion ofretroreflector/obturator may include a mechanical shutter device capableof cycling open and closed within a few milliseconds, or morepreferably, a liquid crystal device (LCD) disposed over theretroreflector portion, such as the LCD-CDS921 06 available from CubicDefense Systems, San Diego, Calif.

However, it should be noted that, for the present invention, it ispreferred that the selection of the retroreflector be tailored to thenature of the use. Specifically, the type of retroreflector used islargely dependent on the speed of the required modulation.

A variety of devices utilizing both “solid state” and “soft” materialsare in use for deflecting or switching optical beams. Solid-statedevices for steering or high-speed modulation of light use acousto-opticbeam deflection, non-linear optical crystals, or optically pumpedcarrier shifting in semiconductors. Soft materials are preferably usedas they offer the advantages of low power consumption and low costprocessing methods such as ink jet deposition, micro contact printing,and self-assembly. Soft devices employ electro-optic polymers, liquidcrystals, and micro-structured composites such as polymer-dispersedliquid crystals and nematic displays.

Polymer dispersed liquid crystals (PDLC) operate on the principle ofelectrically controllable light scattering. These materials are combinedapplication of polymers and liquid crystals, which do not requirepolarizers for its operation unlike nematic displays, thus making themmore transparent with minimum loss of light.

PDLCs consist of liquid crystal droplets that are dispersed in a solidpolymer matrix. The resulting material is a polymer matrix with liquidcrystal droplets filling in the holes. By changing the orientation ofthe liquid crystal molecules with an electric field, it is possible tovary the intensity of the transmitted light.

While manufacturing a polymer dispersed liquid crystal shutter, a fluidmonomer (epoxy resin) and fluid-curing agent (hardener) are mixedtogether with a liquid crystal. As the polymerization proceeds theliquid crystal phase separates from the polymer. The mixture hardens(polymerizes) and locks in nearly spherical droplets of liquid crystalwithin the polymer binder. The arrangement of the liquid crystalmolecules within these droplets depends primarily on the kind of polymerused and on the size of the droplet. Referring to FIG. 6, a schematicdiagram of the polymer-dispersed liquid crystal cell is depicted. Thepolymer-dispersed liquid crystal cell comprises of two or more plates601 stacked and separated from one another by means of liquid crystal602 dispersed in a polymer matrix 603. The plates 601 can be of anytransparent material including plastic and glass. The plates are coatedwith conducting and transparent electrodes 604.

Referring to FIG. 7, a plurality of configurations of liquid crystalmolecules, depicting open and closed optical states, is shown. Manydifferent configurations have been observed and they depend on factorssuch as droplet size and shape, surface anchoring, and applied fields. Aclosed state may occur when the liquid crystal molecules 702 areanchored with their long axes perpendicular to the droplet walls 703with the point defect 704 in the centre of the droplet a radialconfiguration 701. A closed state may occur when the molecules areoriented perpendicular to the droplet wall 707, when there is weaksurface anchoring (axial configuration 705). This configuration resultsin a line defect 711 that runs around the equator of the sphericaldroplet. When an electric field (not shown) is applied to a radialdroplet 701, the molecules adopt the axial configuration 705. The radialconfiguration 701 is returned when the field is removed.

A semi-open, semi-closed state may occur with a bipolar configuration708, which is obtained by tangential anchoring of the liquid crystalmolecules. This creates two point defects 709, 710 at the poles of thedroplet.

Referring to FIG. 8, a typical polymer dispersed liquid crystal sampleis depicted. The PDLC comprises of plurality of droplets 801, 802, 803with different configurations and orientations, i.e., the symmetry axesof these droplets are random. However, when an electric field 804 isapplied the molecules within the droplets 801, 802, 803 align along thefield 804 and have corresponding optical properties. The lines 805 onthe droplet represent the directed orientation.

Unpolarized light 806 entering the polymer-dispersed liquid crystal atnormal incidence to the surface interacts with the droplets 801, 802,803 oriented parallel and perpendicular to the incoming light, as wellas angles in between. Since the symmetry axes are random, it is notpossible for all the index of refractions to be similar. Due to thechange in index of refraction as light traverses the crystal, theincoming light is scattered 807 by most droplets and the PDLC appearsopaque. This property of polymer-dispersed liquid crystal is put to usewhile employing it as a shutter/obturator.

Conversely, on application of electric field 804 the droplets 801, 802,803 in the polymer-dispersed liquid crystal 800 rotate such that theirsymmetry axes are aligned parallel to the field. The ordinary index ofrefraction is matched to the refractive index of the matrix so that in afield ON state the light signals 806 experience the similar index ofrefractions that makes the crystal appear transparent and the light 807is found at the other end of the crystal. Upon removing the field, thedroplets 801, 802, 803 revert back to their random orientation and thedisplay is again opaque. This functionality of opening (transparency)and closing (opaqueness) of polymer-dispersed liquid crystal makes itone of the preferred obturator/modulator types for optical communicationsystem of the present invention.

FIG. 9 is a functional block diagram of a polymer-dispersed liquidcrystal as an obturator/modulator in use. The system comprises of a basestation 901, a transceiver 902 for transmitting 903 and receiving 904interrogation pulse, a remote station 905, an electronic driver 906 anda polymer dispersed liquid crystal 907. The turn-on or switch-on time isinfluenced by the applied voltage level and by the thickness of theliquid crystal layer. The voltage levels are preferably in the range ofCMOS voltages. The retroreflector 908 is arranged behind the liquidcrystal modulator 907.

The polymer-dispersed liquid crystal 907 as mentioned above maintainsthe bistable state of ON and OFF and acts as an obturator forinterrogation pulse stream 903 by blocking and allowing laser signals topass through the crystal 907. The shuttering of the polymer-dispersedliquid crystal is controlled by the obturator signal provided by theelectronic driver 906 capable of delivering voltages corresponding tothe input signal 908. The input signal can be any pulse signalpreferably pulse position or pulse width pulses.

In the absence of a control voltage, or with small control voltagesbelow a threshold voltage, the incoming laser signals 903 are scatteredstrongly. Due to immense scattering the laser signals are not able toreach retroreflector 908 and it does not become effective.

If a voltage, which exceeds the threshold voltage, is applied to theliquid crystal cell 907, the cell 907 becomes transparent and the lasersignals 903 are able to pass through it. Between the two states, apreferably nearly linear section exists, which is used for themodulation of the laser signals 903. Furthermore, if one liquid crystalcell 907 is not sufficient to achieve a high depth of modulation, then aplurality of such cells 907 may be arranged in a row behind one another.

These voltages cause polymer-dispersed liquid crystal 907 to shutter theinterrogation pulse stream 903 passing through it. The modulatedinterrogation beam travels into and is reflected from the retroreflector908. The reflected modulated beam then travels back through, and isagain modulated by the polymer dispersed liquid crystal modulator toproduce the response pulse stream 904 to be sent back to the transceiver902 for identification and range calculations.

In another embodiment, ferroliquid crystals (FLC) can be used asobturator/modulator to achieve faster data rates. FLCs have fasterswitching speeds than other types of liquid crystals and are used tomake optical shutters and switchers (fast modulation of intensity oftransmitted or reflected light as well as the polarization state of“light). Spatial light modulators are also fabricated from FLCs, whichprovide the basis for advanced display technologies (high resolution,wide viewing angle, low driving voltage).

Referring to FIG. 10 a cross-sectional view of the ferroelectric liquidcrystal retroreflector to be used in the present invention is depicted.This device uses a dynamic memory on a very large scale integration(VLSI) backplane to activate the liquid crystal modulator wherein theFLC layer 1007 is sandwiched between the backplane 1008 and a coverglass 1002.

A transparent and conductive indium oxide (ITO) layer 1001 is depositedon the undersurface of the cover glass 1002. This surface is then coatedwith an alignment layer 1003. A preferred alignment material ispolybutylene terephthalate (PBT). A metallic electrode 1005 with anelectrode wire 1004 is mechanically bonded to the cover glass 1002. Thismetallic electrode 1005 is also electrically connected to the ITO layer1001 to produce a transparent top electrode. The ferroelectric liquidcrystal (FLC) layer 1007 is placed within a SiO spacer 1006 between thetop electrode and the VLSI chip 1008.

The VLSI backplane consists of a two-dimensional array of conductivepads acting as electrodes to apply voltage across the FLC layer. Theconductive pads also serve as mirrors that output the modulated signalby reflection, since the VLSI backplane is non-transmissive. Each pad iselectrically connected to an independent dynamic memory cell within theVLSI chip. Each memory cell stores a binary bit of data (i.e., 1 or 0)received from the obturator driver (not shown) in the form of voltages.

These voltages are applied to the conductive pixel pad to produce anelectric field between the pad and the transparent top electrode. Byapplying 2.5 volts to the top electrode, the electric field vectors ateach pixel have equal magnitude, but the electric field vectors changedirection depending on whether the data bit is a 1 or 0. The directionof the electric field vectors switches the FLC into one of two states byinteracting with the polarized FLC molecule to produce either right- orleft-handed torque on the molecule. A FLC molecule is free to rotatethrough small angles and will pivot about the smectic layer normalorientation ([agr].sub.0) until the torque, viscous, and elastic forcesare equalized. This molecular rotation results in a bulk reorientation(or tilt) of the liquid crystal's optical axis. A nonlinear FLC materialacts as a half-wave retarder. A half-wave retarder rotates the light'spolarization by 2[phgr], where [phgr] is the angle between the light'spolarization and the waveplate's optic axis. In the present invention,the polarization of the incident/interrogation beam 1009 is rotated bytwice the-tilt angle ([PSgr]) of the optic axis. For example, if theFLC's optic axis tilts .+−.0.22 degrees about the smectic layer normalorientation, the net change of 44 degrees in the optic axis will rotatethe light's polarization by 88 degrees.

Rotation of the FLC material's optic axis (which is controlled by thedirection of the electric field) produces a change in the light'spolarization. This change in polarization can be converted to amplitudeor phase modulation depending on the orientation of the FLC layer withrespect to the polarization of the incident/interrogation beam 1009. Themodulated beam 1010 is then received by the interrogating device foridentification and range finding.

In another embodiment, a micro-electro-mechanical system (MEMS) deviceis used as obturator/modulator. The Micro-Electro-Mechanical Systemintegrates mechanical elements, sensors, actuators, and electronics on acommon silicon substrate through microfabrication technology. While theelectronic devices are fabricated using integrated circuit (IC) processsequences (e.g., CMOS, Bipolar, or BICMOS processes), themicromechanical components are fabricated using compatible“micromachining” processes that selectively etch away parts of thesilicon wafer or add new structural layers to form the mechanical andelectromechanical devices.

FIG. 11 depicts an arrangement of a MEMS device. It comprises of a base1101, electrodes 1102, micromirrors 1103, and an insulator 1104. Thebase is preferably made of silicon. Between each electrode is a piece ofsilicon oxide, which serves as an insulator 1104 and the base formicromirror 1103.

FIG. 12 depicts an arrangement of the above MEMS device when an electricfield is applied. The electrodes 1202 direct the micromirrors 1203. Whena voltage 1204 is applied to the electrode 1202, the electric fielddeveloped between the micromirror 1203 and electrode 1202 results in themovement of the micromirror 1203. The deflection of mirrors is a fewdegrees. By combining it suitably with the light source, the micromirror1203 reflects incident light into or out of the MEMS device 1201.

The above arrangement can modify an optical beam into a modulated lightstream, each micromirror 1203 forming obturators capable of selectiveactivation or deactivation. The micromirrors 1203 are attached by themeans of any elastic fastening known to those of ordinary skill in theart to enable resisting rotation away from a predetermined rest positionand to selectively control the rotation thereof away from rest position.Micromirrors 1203 are generally placed in the optical paths of lightpulses (not shown) in order to interrupt or modify light paths inaccordance with their positions.

FIG. 13 shows an exemplary embodiment of MEMS working as anobturator/modulator. The MEMS consists of input 1301 and output 1302transparent plates and a wafer 1303 forming a substrate between theplates. Convergent focusing lenses 1304 a and 1304 b, electrodes 1305 aand 1305 b, micromirrors 1306 a and 1306 b, diaphragm 1307 a and 1307 b,and supplementary reflecting surface 1308 a and 1308 b aremicro-machined units of the wafer 1303. Frame 1309 forms a spacersurrounding the network of micromirrors 1306 and maintains a defineddistance between the output plate 1302 and wafer 1303.

In operation, when no voltage is applied the MEMS is in non-activatedstate. The incident light 1310, being initially focused by convergentfocusing lens 1304 a, is sent backwards by the reflecting surface of themicromirror 1306 a, then reflected forwardly by the supplementaryreflecting surface 1308 a and finally sent towards the exterior throughthe diaphragm 1307 a to act as modulated light beam 1311.

Conversely, when voltage is applied, the MEMS device is in activatedstate. Due to application of voltage the micromirror 1306 b is turnedthrough a small angle. The activated configuration leads to a deflectionin the light beam 1312, initially focused by the convergent focusinglens 1304 b and sent back by the reflecting surface present on themicromirror 1306 b, outside the field associated with the supplementaryreflecting surface 1308 b. The latter is thus not in a position to causethe passage of the light through the diaphragm 1307 b, and, as a result,shuttering takes place.

The suppression of the control voltages again resets the micromirror1306 b into its initial position due to the elastic strain forcegenerated in the micromirror 1306 b fastenings. When the voltage iswithdrawn from the MEMS device, it starts transmitting the incidentlight and hence ON-OFF keying of the optical signal can be observed.

The present optical communication system uses pulse position or pulsewidth modulation to control the operation of the electronic driverconnected to MEMS. Each data bit in the obturator driver results in theobturator signal/voltage to provide the activation-deactivationvoltages. The control voltages make the MEMS to shutter theinterrogation pulse stream passing through it. Thus, if the bit isactive, the mirror is turned ON during the bit period and light in theform of interrogation pulse stream is shuttered during this period. Ifthe bit is not active the mirror is turned OFF and the light enters theMEMS to produce the modulated response pulse stream to the source foridentification and range finding.

In another embodiment, multiple quantum wells (MQW) can also be used asretro reflectors wherever there is need for fast data rates. Multiplequantum wells are semiconductor structures composed of alternating thinlayers of two or more different semiconductor materials and, inparticular, of semiconductor materials having differing bandgaps forexample, GaAs, AlGaAs, and InGaAs among others. MQW structures areusually produced using well-known epitaxy techniques, such as molecularbeam epitaxy or metal-organic chemical vapor deposition sometimes knownas organometallic vapor phase epitaxy. Typically, layer thickness is ofthe order 100 Angstroms and a typical structure might comprise 100 suchlayers, resulting in a total thickness of about 1 micrometer.

The advantage of the MQW device technology for an optical communicationsystem is that it operates on low power and can provide fast modulationrates. The maximum speed of a MQW modulator is determined, up to THzrate, by the RC time constant of the device and its driver. Foravailable drivers and MQW structures speed of about 10 MHz is possiblewith a square centimeter aperture device. The optical modulators usingMQW can be designed to be rugged and lightweight.

By coupling MQW technology with optical communications system, opticaltransceiver for secure, high speed data transmission can be produced.These devices require very low power and are less likely to interferewith the surrounding equipment than other devices. MQW devices aregenerally compact, low mass, rugged and environmentally stable.Conventional electronic circuits, such as TTL logic, can power thesedevices. These characteristics make these devices suitable for remotedata transmission from sensitive or high value platforms, such assatellites and unpiloted airborne vehicles.

Referring to FIG. 14 is an exemplary embodiment of Multiple Quantum Wellworking as an obturator/modulator is depicted. The Base stationtransmitter 1401 transmits an interrogation signal 1403 to a remoteobject 1402. The interrogation signal 1403 passes through MQW modulator1404 controlled by an electronic driver 1405, which impart voltagesacross MQW modulator 1404 corresponding to input signal 1406. Thesevoltages cause MQW modulator 1404 to shutter the interrogation lightpassing through it, resulting in a modulated interrogation beam 1407 andis then reflected back.

The reflected modulated beam 1407 after that travels back through, andis again modulated by MQW modulator 1404, thus reinforcing the originalmodulation. After passing through the MQW modulator 1404 for a secondtime, reflected modulated beam 1408 finally travels to the base stationreceiver 1409 for identification and range calculations.

It is important to note that the selection of the retroreflector islargely dependent on the nature of use and rate of modulation required.For example, as we move from PDLC to FLC to MEMS to Quantum Well, themodulation rate keeps on increasing and it ranges from 1 KHz in case ofPDLC to 1 GHz in Quantum Wells.

In each of the above embodiments, the optical retroreflectors may betemperature stabilized with a thermoelectric cooler and/or a resistiveheater to optimize the contrast ratio for a given operating environment.In addition to or in place of such devices, as discussed above, a biasvoltage may be applied to the device and adjusted to compensate fortemperature changes by a small battery delivering the required power.The time taken to heat the crystal is approximately 0.9 milliseconds.

In one embodiment, a PDLC is used in an environment having an ambienttemperature at or below 20 degrees Celsius. To minimize the drain on thevoltage source, such as the battery, the heating is preferably done onlywhen the device, or the user operating the device, recognizes that anincoming communication signal has been recognized and a communicationchannel needs to be established. For example, in a secure covertoperation, as described below, the heating element will activate afteran initial transmit signal is positively identified by a response unit.Upon such recognition, the optical retroreflector will activate the PDLCheater in order to warm the PDLC unit up, if the temperature is below 20degrees Celsius. Because the heater can take 10 to 60 ms to bring thetemperature of the PDLC up to the point that it can effectively operatein the required response time, it is preferred to have the transmitsignal repeat several times, thereby being ready to correctly modulatethe response pulses in subsequent transmissions.

In one embodiment, a heating element is integrated with retroreflectorsof the present invention. A user activates the heating element, toprepare for a known optical transmission. Alternatively, an opticaltransmission can include an initial interrogator message acting as awakeup message. The wakeup message causes the heating element to beactivated, i.e., a voltage source, and for heat to be applied to theretroreflector, i.e., by subjecting it to a bias voltage. The rapidheating process, preferably taking less than a few milliseconds, enablesimproved operational performance, thereby allowing the system to worksubstantially optimally even if the temperature drops below a certainthreshold level.

The retroreflector and range finding system, disclosed in the presentinvention, can be exploited in an assortment of applications including,ground to air, ground to space, air to air, air to space and space tospace data transmission, and, more, specifically but not limited to,secure covert operations, microsatellites, dynamic optical tags (DOTs),and tetra hertz operational reachback (THOR). The following sectiondescribes a few embodiments where the above described integrated laserrange finding and optical communication system can be used.

Secure Covert Operation

One embodiment of the present invention is directed toward a securecovert operation for combat comprising a combat response unit having ahelmet-mounted challenge receiver and a retroreflector/obturator,including the steps of projecting a high pulse laser signal and atransmitted code of the day (TCOD) onto the combat response unit from acombat interrogatory unit, receiving the laser transmit signal and TCODat the challenge receiver, selectively reflecting the laser transmitsignal by opening and closing the retroreflector/obturator according toa response code of the day (RCOD), receiving the reflected lasertransmit signal and RCOD at the combat interrogatory unit, and combiningthe received RCOD with the TCOD to identify the combat response unit andits position. The present invention can be used, therefore, to conductlaser range finding, perform code transmissions, and conduct voicecommunications.

FIG. 15 illustrates the operation of the combat identification system ofthis invention. The combat interrogatory unit 1520 of this invention isshown in a preferred weapon-mounted disposition where the challengingsoldier may target the helmet-mounted combat response unit 1522 of thisinvention worn by a soldier in a combat simulation exercise or in actualcombat. One of ordinary skill in the art would appreciate that theresponse unit 1522 could be mounted in any location proximate to or onthe soldier, including a vest, belt harness, or other device. Furtherone of ordinary skill in the art would appreciate that the response unit1522 could be mounted to an object, such as a tank, building,conventional transceiver, vehicle, plane, or other structure.

An infrared (IR) transmit signal 1524 is projected by unit 1520 uponoperator command. Transmit signal 1520 radiates outward along a narrowbeam, eventually illuminating response unit 1522. For example, transmitsignal 1524 may be embodied as a 6-milliradian beam of 1540 nm IR light,which then illuminates an area of about 6 meters on a side at a typicalweapon range limit of 1000 meters. Upon being received, detected andverified at response unit 1522, transmit signal 1524 is thenretroreflected back to interrogatory unit 1520 as the response signal1526. For a 6-milliradian transmit signal 1524, response signal 1526includes a reflection of, for example, a 1.5-centimeter portion of the6-meter transmit beam 1524. This 1.5 cm reflected portion includes about0.002 percent (−47 dB) of the initial energy of transmit signal 1524,which is generally reflected back to interrogatory unit 20 by aprecision retroreflector. Response signal 1526 is received atinterrogatory unit 1520 reduced by an additional −8 dB, which leavessufficient power for combat personnel detection and processing atinterrogatory unit 1520. The 1540 nm signal wavelength is preferredbecause it is eye-safe and has relatively low absorption and scatteringloss in the usual battlefield smoke and haze.

Operationally, the user can choose to use the signal in order todetermine the range of a combatant, tank, building, truck, vehicle, orother object, as previously discussed, or as a mechanism to communicateimportant information, including but not limited to, codeidentifications, such as whether the individual is a “friend” or “foe,”and audio communications.

When used to communicate code identifications, the present invention canmodulate code signals, including transmit and receive code signals, onto the laser signal. FIG. 16 is a schematic diagram illustrating theoptical operation of a response unit. As described in detail here inbelow in connection with FIG. 19, transmit signal 24 includes a transmitcode of the day (TCOD) including a frame-synchronization preamble (notshown) followed by a TCOD 24(a) followed by a TCOD interrogation pulsestream 24(b). In operation, TCOD 24(a) is received by one or more of theplurality of IR sensors 30 and presented to the challenge receiver 46for verification. When TCOD 24(a) is verified, challenge receiver 46produces a response code of the day (RCOD) signal 48, which includes alogical combination of selected information from TCOD 24(a) and from thelocal memory of challenge receiver 46 (not shown) that is described indetail herein below. RCOD signal 48 is presented to the obturator driver50, which produces an obturator signal 52 for opening and closing(making translucent and opaque) the obturator 54 in each of theplurality of retroreflector/obturators 32.

To provide for a secure communication and identification system, it ispreferred that the present invention is not operable, nor are therelated algorithms or source codes available, through reverseengineering in an instrumented lab. If an embodiment of the presentinvention could be made operable by an individual who is not authorizedto operate the device or if that unauthorized individual could accessthe methods and/or codes used to drive the device, the security of thesystem would be compromised. To avoid compromising security, it ispreferred that the system uses narrow laser beams for bi-directionalcommunications; a secret rolling code of the day that changes over apre-designated time period and is only known to authorized persons; arandomly generated number that is known to the interrogator andreceiver; processes that utilize encryption of the COD by the RGN inboth directions; identification methods, such as fingerprints, voice, ormanual keying, to determine if an authorized person is using the weapon;hardware with a secure area; and self-destruct mechanisms to destroysoftware and codes upon deconstruction of the device.

A biometric identification (ID) signal 56 is also presented to obturatordriver 50 to enable or disable operation thereof based on theverification of a scanned thumbprint input by the dismounted soldier inpossession of helmet-mounted response unit 22, which is furtherdescribed herein below in connection with FIGS. 17 and 20( a)-(d). RCODsignal 48 includes a delay and a response pulse stream 26(a). The RCODdelay is sufficient to permit TCOD interrogation pulse stream 24(b) toarrive at reflector/obturator 32. Obturator 54 is then cycled open andclosed in accordance with obturator signal 52 to produce response pulsestream 26(a) by reflecting selected elements of interrogation pulsestream 24(b) from the retroreflector 58 in at least one of the pluralityof retroreflector/obturators 32.

One of ordinary skill in the art would appreciate that variousidentification measures could be used to insure the operator of theresponse unit or interrogator unit are authorized users, including theuser's voice pattern, or a keyed in verification input, i.e., apassword. For example, a transceiver integrated with a memory andprocessor could be used to recognize an authorized voice pattern. If areceived audio input matches a stored pattern, the processorcommunicates a positive signal 58 back to the to obturator driver 50.Similarly, a keypad in data communication with a memory and processorcould be used to receive a data input from a user. If the data inputmatches an authorization code stored in the memory, the processorcommunicates a positive signal 58 back to the to obturator driver 50.

Additionally, the identification measures could optionally be subject toa timer that requires the user to periodically demonstrate that he orshe is, in fact, an authorized user. The timer is programmed to activatea verification process on a periodic basis, such as once every 24 hours.The verification process requires a user to input identification data,such as biometric or personal data, into the unit or indicate activity,i.e., through motion, via motion sensors. Entering this verificationinformation in time will ensure the unit retains the codes used togenerate the transmit signal. Failure to enter this information in timewill cause the unit to turn off the use of codes or possibly destroy theexistence of codes under the assumption that the unit has fallen outsideof the possession of an authorized user and must therefore be strippedof its codes.

FIG. 17 is a schematic diagram illustrating the logical operation of aresponse unit. The elements of FIG. 17 are arranged in three functionalcategories for clarity; (a) helmet sensors, (b) helmet logic and (c)helmet memory. In operation, helmet-mounted response unit is firstprogrammed with certain biometric data unique to the user and with acode of the day (COD), which includes a challenge code (CC) followed bya response code (RC). The helmet is then donned by the user according toa predetermined anti-spoofing protocol. The donning soldier first passeshis/her thumb over a biometric thumbprint sensor 60 in a manner (knownonly to the soldier) for which response unit 22 has previously beenprogrammed. Biometric thumbprint sensor 60 produces the coded biometricdata stream 62, which is immediately evaluated by the biometricidentification logic 64. This evaluation involves comparing data stream62 to the earlier-stored thumbprint scan, data 66 for the donningsoldier to produce an enable/disable decision. If logic 64 decides thatthe thumbprint scan fails, the soldier may be afforded, for example, twoadditional opportunities to enable the helmet-mounted response unit bymeans of an audible or visual indicator (not shown). After twoadditional attempts, logic 64 decides that the biometric ID is invalid,and sets biometric ID signal 56 to “disable” obturator driver 50,permanently shutting obturator 54 to prevent any retroreflection.Moreover, biometric ID signal 56 may also be presented to aself-destruct timer 67, which begins a logic and memory self-destructioncountdown. When completed, this countdown triggers the erasure of alllogic and data stored in the helmet memory, thereby making a capturedhelmet-mounted response unit worthless to an enemy. The helmetelectronics may easily be reprogrammed by the friendly forces for use inanother combat exercise or the like.

After successfully completing a thumb scan and donning the helmet,biometric ID signal 56 is set to “enable” and obturator driver 50 isenabled so the soldier is thereafter equipped to passively respond tovalid incoming interrogatory signals in the manner now described. Whenthe soldier again doffs the helmet, the helmet-doffing sensor 68immediately signals logic 64, which resets biometric ID signal 56 to“disable” and obturator driver 50 is again disabled, permanentlyshutting obturator 54 to prevent any retroreflection.

In use, a response unit first begins the secure covert communicationupon the arrival of IR transmit signal 24 from interrogatory unit 20.TCOD 24(a) is received by at least one IR sensor 30, which produces asignal 70 that is presented to the signal verification and decodinglogic 72. The relative location on the helmet of the particular IRsensor 30 receiving the signal is identified in logic 72 to determinethe arrival quadrant (Front, Right, Rear, or Left) of IR transmit signal24. This arrival quadrant information may be used in logic 72, forexample, to bias other processing parameters or to signal the helmetedsoldier, by audible or visual means, of the arrival quadrant so thatappropriate action may be undertaken (such as, for example, skepticalevasion of interrogatories arriving from behind enemy lines).

TCOD 24(a) is validated by examining it to verify that it includes avalid CC followed by a randomly generated number (RGN). This isaccomplished by comparing the received CC with the CC portion of the COD74 stored in the helmet and accepting the RGN if the incoming CC matchesthe stored Cc. The entire stored COD 74 and the incoming RGN are thenpassed as a data signal 76 to the response code of the day (RCOD)generation logic 78, which creates the RCOD 80 by combining the CC andRC portions of the stored COD with the PRN in a predetermined manner.After generation, RCOD 80 is passed to obturator driver 50 for use inopening and shutting obturator 54 accordingly. The first portion of RCOD80 is a closed shutter interval that is computed as a combination of thestored RC and the incoming RGN. The second portion of RCOD 80 is anopen-shutter interval that is determined by some portion of the CC. RCOD80 is synchronized to begin at a predetermined interval (such as 10 ms)after the end of the incoming TCOD so that the interrogator may evaluateRCOD 80 to verify that the reflecting response unit is a mend and not afoe, thereby completing the IFF transaction.

FIG. 18 is a schematic diagram illustrating the logical operation ofinterrogatory unit. The elements of FIG. 18 are arranged in threefunctional categories for clarity; (a) interrogator sensors/emitters,(b) interrogator logic and (c) interrogator memory. In use, aninterrogatory unit first begins the secure covert communication when thetrigger sensor 82 detects a command from the operator to interrogate atarget. Trigger sensor 82 produces a signal 84 that is presented to theTCOD generation logic 86, which responsively retrieves a locally-storedcopy of the COD 88 and a RGN 90 from a pseudorandom number (PRN)generator 92. TCOD generation logic 86 then combines the CC portion ofCOD 88 with RGN 90 to produce the TCOD portion of TCOD 94, which is thenfollowed by the TCOD interrogation pulse stream. TCOD 94 is thenamplified as necessary to drive the TCOD projector 96, which producesthe IR transmit signal 24, initiated with the frame-synchronizationpreamble (not shown), and directs it to the target. TCOD is alsopresented to the signal decoder and verifier logic 98 for use inprocessing any incoming IR signals received at the IR sensor 100. Whenthe TCOD portion of TCOD 94 is transmitted (see FIG. 19), logic 86notifies logic 98 of the start of the response interval. Any incomingresponse signal 26 at RCOD sensor 100 produces a RCOD signal 102 that ispresented to logic 98 for evaluation. Logic 98 reverses the encodingprocess discussed above in connection with FIG. 17 and below inconnection with FIG. 19.

RGN 90 and the RC from COD 88 are used to compute the properclosed-shutter interval, which is compared to the delay interval betweencompletion of the transmission of TCOD 94 and the beginning of responsepulse stream 26(a). The appropriate elements of COD 88 are then used tocompute the proper open shutter interval, which is then compared to theactual length of the incoming response pulse stream 26(a). If the twocomparisons are not successful, logic 98 does nothing; leaving thedisplay 104 inactive. When the comparisons are both successful, logic 98produces an indicator signal 106, which activates display 104, therebycompleting the transaction. Display 104 may be a simple light-emittingdiode (LED) indicator or an audible signal or any other useful indicatorconsistent with requirements for security and covertness.

As described above in connection with FIG. 17, an interrogatory unit mayalso include anti-spoofing means to prevent use by an enemy of acaptured interrogatory unit. A biometric sensor 108 may be used toaccept thumbprint or fingerprint input or retinal image input or anyother useful biometric data unique to the authorized operator. Uponactivation, biometric sensor 108 presents the incoming biometric data110 to the biometric ID logic 112 for comparison to the biometric IDdata 114 stored previously by the same soldier. If, at some point, logic112 decides that the biometric ID is invalid, a biometric ID signal 116is set to “disable” and TCOD generator logic 86 is disabled, permanentlyshutting down TCOD projector 96. Moreover, biometric ID signal 116 mayalso be presented to a self-destruct timer 118, which begins a logic andmemory self-destruction countdown. When completed, this countdowntriggers the erasure of all logic and data stored in the interrogatormemory, thereby making a captured weapon-mounted interrogatory unitworthless to an enemy. The interrogator electronics may easily bereprogrammed by friendly forces for use in another combat exercise orthe like.

After successfully completing a biometric scan, biometric ID signal 116is set to “enable” and TCOD generator logic 86 is enabled so the soldieris thereafter equipped to actively interrogate targets in the mannerdescribed above. After a predetermined period of inactivity, establishedby, for example, a simple timer (not shown), logic 116 resets biometricID signal 116 to “disable” and TCOD generator logic 86 is againdisabled, permanently shutting down TCOD projector 96.

FIG. 19 is a chart illustrating the relationship between exemplaryembodiments of the COD 120, the TCOD 122 and the RCOD 124 of thisinvention. Each of the six symbols of COD 120 and TCOD 122 are 7-bitvalues (ranging from 0-127) encoded as pulse positions within a 36microsecond frame interval, which is established and synchronized foreach transaction by a three-pulse TCOD frame-synchronization preamble(not shown). Each pulse is 66.67 ns in duration, which allows the use ofan inexpensive microprocessor (not shown) for implementing the variouslogic described herein.

The position of a pulse within a frame represents the corresponding7-bit symbol. COD 120 is changed daily and all interrogatory units andresponse units in a system are updated daily with the new COD 120. COD120 includes a 4-symbol CC 126 and a 2-symbol RC 128. TCOD 122 includesCC 126 and a 2-symbol RGN 130 followed by a 10 ms buffer intervalfollowed by TCOD interrogation pulse stream 132 consisting of a 50 msstream of I-ms spaced pulses. RCOD 124 includes a delay 134 during theclosed-shutter interval followed by a response pulse stream 136 duringthe open shutter interval. Delay 134 is computed by dividing theabsolute value of the difference between RGN 130 and RC 128 by ten andadding 10 ms, providing a range of values from 10-20 ms in 1 ms steps.This coding method is both secure and covert because RGN 130 is sharedonly by the interrogator and target even though COD 120 is known by allfriendlies. Although interception of RGN 130 is unlikely because of thenarrow TCOD beam (3 milliradians), any such interception is uselesswithout prior knowledge of COD 120 because RC 128 is not transmitted andboth RC 128 and RGN 130 are required to compute delay 134. The openshutter interval that reflects response pulse stream 136 is computed inmilliseconds by adding three times the fourth digit of CC to five,giving a range of values from 5 to 32 ms in 3 ms steps.

Thus, the duration of response pulse stream 136 cannot be spoofedwithout prior knowledge of COD 120 or interception of TCOD 122 and theduration of delay 134 cannot be spoofed without having both the priorknowledge of COD 120 and the successful interception of TCOD 122. Suchspoofing also presumes prior knowledge of the decoding algorithmsdescribed above. Each transaction is completed within 60 ms. Aninterrogator may repeat an interrogation as desired to reduce theprobability of false negatives. Assuming that interrogation is repeatedup to four times before accepting a negative (partial response) result,the entire transaction is completed within 250 ms. This method ofobtaining a response is necessary only under extreme scintillation andrange conditions, at the limits of link performance.

FIGS. 20( a)-(d) show several examples of suitable means for acceptingbiometric data for helmet-mounted response unit. One suitable device foraccepting biometric fingerprint or thumbprint data is the FCD4B14FingerChip™ available from AtMel Corporation, San Jose, Calif. Asdepicted in FIG. 20( a), the print sensor 138 is disposed such that afinger 140 may be drawn across print sensor 138 while in continuouscontact therewith. Continuous contact is important and is facilitated byproviding a curved surface 142 generally as shown. As finger 140 movesover print sensor 138, a stream of digital biometric data is produced byprint sensor 138 and presented on a data bus (not shown) formanipulation by microprocessor-controlled logic (not shown). Clearly theexact biometric data stream depends not only on the fingerprint but onthe direction and manner in which finger 140 is drawn across printsensor 138. This is an important feature of this invention because itadds considerable security to helmet-mounted response unit in that theavailability of the proper finger or thumb alone is insufficient tosatisfy the biometric security requirement; the user must also recalland repeat with reasonable accuracy the exact manner in which the thumbor finger was drawn across print sensor 138 when first storing theuser's biometric ID data in response unit.

FIG. 20( b) shows another mounting arrangement suitable for print sensor138, although the curved surface 142 is preferable. FIG. 20( c) showsyet another example employing the curved surface 144, which importantlypermits continuous contact between finger 140 and print sensor 138 whilemoving thereover.

FIG. 20( d) demonstrates an exemplary arrangement for placing printsensor 138 within helmet-mounted response unit so that the user may drawthe thumb 146 over print sensor 138 while grasping helmet-mountedresponse unit 22 preparatory to donning same. Any useful audio and/orvisual indicator means (not shown) may be provided to inform the userthat helmet-mounted response unit has been successfully activated,thereby affording the opportunity to retry activation by repeating themovement of thumb 146 across print sensor 138. If desired, repeatedattempts may be accumulated against a limited number followed byself-destruction of all logic and data stored in helmet-mounted responseunit.

In an alternative embodiment of a helmet-mounted response unit, thebiometric data necessary to identify several members of a combat unitmay be stored in biometric ID storage 66 so that any combat unit membermay activate a helmet-mounted response unit. This permits a member ofthe combat unit to “borrow” the helmet and its response unit fromanother member of the same combat unit and successfully activate it foruse in the battlefield. The size of the group of authorized users islimited only by the memory available in biometric ID storage 66, whichmay be loaded by mass-transfer of digital data collected from thethumb-scans of all members of the combat unit. Similarly, in analternative embodiment of an interrogatory unit, the biometric datanecessary to identify several members of a combat unit maybe stored inbiometric ID storage 114 thereby permitting a member of the combat unitto “borrow” the weapon and response unit from another member of the samecombat unit and successfully activate it for use in the battlefield.

FIG. 21 is a block diagram showing a flow chart exemplifying the covertcommunication transaction method of this invention. This process beginswith the step 148 where the interrogating soldier triggers aninterrogation command at an interrogatory unit. In the step 150, a TCODis created by accepting the RGN produced in the step 152 and the CODretrieved from local memory in the step 154. In the step 156, an IRtransmit signal encoding the TCOD is projected to the targeted responseunit. In the step 158, the TCOD is received at the targetedhelmet-mounted response unit. More precisely, the 3-pulse frame-synchpreamble and the first six symbols of the TCOD are first received anddecoded in step 158, which may also include an arrival quadrantindication step (not shown) to notify the helmet wearer by some usefulmeans of the quadrant (Front, Right, Rear, or Left) from which thereceived TCOD has arrived.

In the step 160, the received TCOD is validated by first verifying thatthe biometric security has been satisfied in the step 162 and thenretrieving from local storage the COD in the step 164. As describedabove in connection with FIG. 19, the CC (the first four symbols fromthe COD) is compared with the CC from the received TCOD and, if matched,the next two symbols of the received TCOD are decoded as the RGN in thestep 166. In the step 168, the RGN From step 166 and the RC (the fifthand sixth symbols of the COD) are used to compute the closed shutterinterval (the delay interval) of the RCOD and the fourth symbol of theCOD is used to compute the open shutter interval (the response pulsestream) of the RCOD. In the step 170, the RCOD from step 168 is used tocycle the obturator, thereby retroreflecting the interrogatory pulsestream portion of the TCOD according to the RCOD.

In the step 172, the RCOD is received and decoded at the interrogatoryunit and validated in the step 174, which uses the locally-stored RGNand COD retrieved in the step 176 to duplicate thy computations used tocreate the RCOD at the response unit and to compare the received RCODwith the locally-computed RCOD. In the step 178, the results of step 174are evaluated to make a friend or foe decision, completing thetransaction initiated in step 148. If Friend, then the step 180 signalsthe interrogatory unit user in some useful manner, such as lighting upan LED for a short time. If Foe, then the step 182 initiates arepetition of the transaction (with a new RGN) or does nothing, therebyindicating that the transaction has failed to identify a friend.

One of ordinary skill in the art would appreciate that, eitherseparately or in concert with the above communication scheme, other datacan be modulated on to a signal and received at a receiver unit. Suchdata can include, but is not limited to, audio, text, and/or images.

Dynamic Optical Tags

Another application of the present invention is in enabling the use ofdynamic optical tags (DOTS). As defined by the Defense Advance ResearchProjects Agency (DARPA), a DOT is preferably a small, thin,environmentally robust, long lived, modulated optical retroreflectingtag working in conjunction with a long range interrogation system.Operationally, DOTS are passive (i.e., in the sleep mode) and are onlyactivated when interrogated. When active, a DOT modulates anilluminating beam to transmit coded information onto a retro-reflectingpath. Preferably, a DOT is non-RF to avoid depending upon radiofrequencies that can be detected by the tagged target or by thirdparties in the area of the emitter.

When affixed to an object, a DOT provides a tracking entity the abilityto uniquely identify and locate the object. As the object on which thetag is mounted moves through a region, the DOT can record locationinformation (via a global positioning satellite receiver), imagery,temperature, pressure, audio, and other data that can provideinformation about the object, the conditions under which it wassubjected, its location and its state.

In one embodiment, a DOT is a retroflector/obturator capable of rapidmodulation is used, such as a Tech Spec™ Corner Cube Retroreflector(Trihedral Prisms) available from Edmond Industrial Optics, Barrington,N.J. The obturator portion of retroreflector/obturator may include amechanical shutter device capable of cycling open and closed within afew milliseconds, or more preferably, a liquid crystal device (LCD)disposed over the retroreflector portion, such as the LCD-CDS921 06available from Cubic Defense Systems, San Diego, Calif.

As previously shown in FIG. 9, one embodiment of a DOT can comprise of abase station 901, a transceiver 902 for transmitting 903 and receiving904 interrogation pulse, a remote station 905, an electronic driver 906and a polymer dispersed liquid crystal 907. The turn-on or switch-ontime is influenced by the applied voltage level and by the thickness ofthe liquid crystal layer. The voltage levels are preferably in the rangeof CMOS voltages. The retroreflector 908 is arranged behind the liquidcrystal modulator 907. The polymer-dispersed liquid crystal 907 asmentioned above maintains the bistable state of ON and OFF and acts asan obturator for interrogation pulse stream 903 by blocking and allowinglaser signals to pass through the crystal 907. The shuttering of thepolymer-dispersed liquid crystal is controlled by the obturator signalprovided by the electronic driver 906 capable of delivering voltagescorresponding to the input signal 908. The input signal can be any pulsesignal preferably pulse position or pulse width pulses. Preferably, aDOT used in the present invention is not larger than 25 mm×25 mm×5 mm;operates in an environment ranging from minus 70 Celsius to 45 degreesCelsius; has an angle of regard of plus or minus 60 degrees or greater;and modulates at least 100 kbits/sec. To the extent the liquid-crystalchosen does not effectively operate in low temperatures, one of ordinaryskill in the art would appreciate that a heating element, as previouslydescribed, could be incorporated to enable effective operation of theliquid-crystal system.

Information stored by, or within, a DOT can be remotely read using thepresent invention. Referring back to FIG. 1, a functional block diagramof the interrogator system 100 of the present invention is shown. Thesystem 100 comprises a laser 110, an optical transmitter 120, an opticalreceiver 130, a light sensitive detector 140, a change-over and acorrelator module 150. The correlator module 150 further comprises aclock signal generator 165 that provides working clock signals to ananalog-to-digital converter 170, a counter 160 for addressing andsequencing a memory module 155 and a processing unit 175. The memorymodule 155 stores digitized values of a sequence of transmission pulsess(t), for triggering the laser 110, as well as reception pulses r(t)outputted from the detector 140 and digitized by the analog-to-digitalconverter 170.

Referring to FIG. 4, a visual representation of one embodiment of thesystem is shown. A laser emits optical signals through a collimator 410which collimates the beam for subsequent transmission through a laseraperture 405. Power is supplied to the unit by battery 480. The systemfurther comprises a HV supply 430, an analog board 440, an APD receivermodule 450, a receiver lens and filter assembly 460 and a receiveraperture 470 into which reflected optical signals are received. Theresulting range is depicted on a range display 420.

Operationally, an aircraft is tracking a tagged cargo container and atagged tank. In operation, a tag is placed on both the container andtank. The tag is a modulating dynamic optical tag that is small, thinand retroreflecting. The tag remains in passive mode (sleep mode) formost of its operation and it is activated when interrogated by a highpulse laser beam, preferably emitted from the tracking aircraft. The tagthen starts modulating the illuminating beam to transmit codedinformation, such as stored data detailing temperature, time, pressure,movement, location, and other characteristics, on the retro-reflectingpath for identification and range finding in accordance with theprinciples of the present invention. The interrogator system thenfurther transmits and/or displays acquired data, including range fromthe object, temperature, time, pressure, movement, location, and othercharacteristics. Preferably, the interrogator system supports acommunication range of 1 kilometer or greater, uses less than 800 wattsof prime power, and weighs less than 25 kilograms. More preferably, anairborne interrogator supports greater than 10 Km range at communicationrates greater than 100 Kbps.

Dynamic Optical Tag enabled optical communication system of the presentinvention results in a small, thin, environmentally robust, modulatedoptical retroreflecting tag and a long-range interrogation system. Inaddition, this enables highly precise tag location along with reliableand efficient information flow between the tags and the interrogationdevice operating in non-RF and visually non-alerting mode.

Terra Hertz Operational Reachback

Another embodiment of the present optical communications system may beapplied to achieving the objectives of DARPA's Terra Hertz OperationalReachback, THOR, program, thereby overcoming the disadvantages ofconventional communication systems. THOR attempts to create a mobile,free space, optical network having data transfer rates of 10 gigabitsper second and an aircraft to aircraft link distance of approximately400 kilometers.

An optical communications system implementing THOR uses aerial opticaltransmissions to establish a link that extends from, a terrestrial pointof presence to an underwater vehicle via an aircraft or spacecraftsurrogate with an air to air relay link so as to track target objectssuch as tanks, aircrafts, forces, ships, subsurface vehicles etc. Inoperation, target objects have the retroreflectors attached therewith.Interrogation signals from aircraft, preferably high pulse rate lasersignals, are modulated-reflected by the retroreflector back to theaircraft for identification and range finding in accordance with theprinciple of the present invention. THOR, unlike GPS systems, does notget jammed during warfare, clouds or turbulences.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention. Forexample, other configurations of combat identifications, secure covertoperation, dynamic optical tags, and terra hertz operational reachbackcan also be considered. Therefore, the present examples and embodimentsare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein, but may bemodified within the scope of the appended claims.

1. A system for communicating information from a first entity toward asecond entity using focused laser light, the laser system comprising: aprocessor configured to provide a coded pulse sequence; a lasercommunicatively coupled with the processor and being configured togenerate a plurality of transmission pulses corresponding with the codedpulse sequence; and an optical transmission system being configured todirect the transmission pulses emitted by the laser toward a targetobject as a beam of light with a beam divergence of less than about 6milliradians.
 2. The laser system of claim 1 wherein the laser is a fastpulsed laser.
 3. The laser system of claim 1 further comprising memoryconfigured to store coded pulse sequences, wherein the processorprovides coded pulse sequences to the laser by retrieving the pulsesequence from memory.
 4. The laser system of claim 1 wherein the laseris any one of a mode-locked visible-range titanium-doped sapphire laser,Kerr lens mode-locked laser, polarization-sensitive mode-locked fiberlaser, or actively mode-locked laser.
 5. The laser system of claim 1further comprising: a light sensitive detector; a change-over module;and a correlator module.
 6. The laser system of claim 1 wherein thelaser generates a plurality of transmission pulses at fast rates andwherein the laser is triggered by coded pulse sequences read out from amemory at a predetermined clock frequency.
 7. The laser system of claim6 wherein the coded pulse sequence for triggering the laser is of apseudo random binary type.
 8. The laser system of claim 6 wherein thecoded pulse sequence for triggering the laser is encoded using a MaximalLength Sequence.
 9. A method of determining range of a target object,comprising the steps of: generating transmission pulses at fast rates bytriggering a laser using coded pulse sequences read out from a memory ata predetermined clock frequency; storing the coded pulse sequences fortriggering the laser; focusing the transmission pulses toward a targetobject as a light beam using a laser.
 10. The method of claim 9 whereinsaid focusing of the transmissions pulses, provides the light beam witha beam divergence of less than about 6 milliradians.
 11. A communicationmethod using a laser system, comprising: generating transmission pulsesat fast rates by triggering a laser using coded pulse sequences read outfrom a memory at a predetermined clock frequency; modulating a signalonto said transmission pulses; and focusing the transmission pulses fromthe first entity toward the second entity using the laser.
 12. Themethod of claim 11 wherein the focusing focuses the transmission pulseas a light beam with a beam divergence less than or equal to about 6milliradians.
 13. The method of claim 11 wherein said communication dataincludes any one of audio, video, text, or image data.
 14. The method ofclaim 11 wherein the laser is any one of a mode-locked visible-rangetitanium-doped sapphire laser, Kerr lens mode-locked laser,polarization-sensitive mode-locked fiber laser, or actively mode-lockedlaser.
 15. An interrogator system for communicating information from afirst entity toward a second entity using focused laser light, thesystem comprising: a laser configured to illuminate a target with acollimated laser light beam; means for providing a transmission pulseswith coded pulse sequences to the collimated laser light beam;modulating means for modulating a signal onto the transmission pulses;and focusing means for directing the collimated laser light beam towardthe second entity.
 16. The interrogator system according to claim 15further comprising a sensor configured to receive an optical signal fromthe second entity; and a processor communicatively coupled with thesensor and configured to determine the range between the interrogatorsystem and the second entity.
 17. The interrogator system according toclaim 15 further comprising a sensor configured to receive an opticalsignal from the second entity; and a processor communicatively coupledwith the sensor and configured to determine the identity of the secondentity from the optical signal received from the second entity.